some dacs are just dacs, no amp included. centrance dacport lx and cypher labs algorhythm solo are a few examples.

im using the dacport lx with my dt880 250's, with a vintage stereo receiver acting as the amp. sounds great, definitely an upgrade from my fiio e07k. Ive never heard the e12, so i don't know how it might sound with a separate dac.

You must get a DAC. That's for sure. Because onboard sound cards are pretty bad. DAC is important to get a clean audio. I still think the Fiio E17 for you. And Audinst MX-1. You can use your E12 with these. I don't know about stand-alone DAC's. CrocCap gave some examples.